1. Field of the Invention
The present invention relates to a method for electrically addressing fluorescent display elements and a display element, and more particularly, to a method for electrically addressing fluorescent display elements to which display technologies such as organic light-emitting diode display (OLED) and the like are applied, and a display element.
2. Description of the Related Art
Display technologies such as a liquid crystal display (LCD), a field emission display (FED) and vacuum fluorescence display (VFD) as well as organic light-emitting diode display (OLED) constitute the general state of the art and have already been applied.
An LCD has a drawback in that there is an aligned monodomain of a liquid crystal between polarizers in an idle state. The alignment of this domain can be changed by means an applied electric field. In this case, the light absorption based on the combination of liquid crystal and polarizers is changed.
LCD displays dominate the market for flat-type displays and monitors. The LCD displays require low energy consumption when ambient light is present. However, if this is not the case, power consumption for additional lighting is required. Also, fast-moving images may be distorted due to a narrow angle of viewing and a low-switching speed of liquid crystals.
In the case of a VFD, electrons are emitted from a heated grid cathode under vacuum. The emitted electrons are accelerated by an electric field and collide with a light-emitting phosphor layer. This operating mode is similar to that of a picture tube.
In the case of an FED, electrons are emitted from a cold cathode array under vacuum in a strong electric field and collide with a phosphor layer, leading to light emission.
The VFD and FED are unfavorably thick for use as display elements, have relatively high operating voltages and a high input power for heating the cathode, particularly in a VFD, and are unsuitable as flexible displays.
OLEDs require injection of charge carriers for forming an excited state by recombination of charge carriers. The excited state decays under light emission (see EP 0423 283, U.S. Pat. No. 5,869,350 and EP 029 40 61). The OLEDs have a very short switching time and a wide angle of viewing. Compared with LCD displays requiring additional lighting, the OLEDs, which do not require adequate ambient light, consume less power. These advantages, however, are canceled when intense ambient light prevails. This is because visually sensed contrast is lowered due to the effect of ambient light.
In addition to the above-described generally known emissive operating modes, the effect of fluorescence quenching due to an electric field has been described in a doctoral thesis by Martin Deussen, Marburg University, 1995. This effect is applied to display elements similar to or identical with OLED display elements.
To solve the above problem, it is an object of the present invention to provide a fluorescent display element and a method for addressing fluorescent display elements which can maintain visually sensed contrast at a constant level regardless of a change in the intensity of ambient light and can reduce power consumption.
To achieve the above object, there is provided a method for electrically addressing a display element based on polymers and/or low molecular-weight organic materials by a fluorescence quenching effect due to an electric field. The method includes the steps of changing positive voltages applied to bright pixels to be inversely related to the intensity of ambient light, and changing negative voltages applied to dark pixels to be related to the intensity of ambient light, whereby an organic light-emitting diode display (OLED) mode and a field quenching photoluminescence emission device (FQPED) mode are performed according to the intensity of ambient light of the display element.
According to another aspect of the present invention, there is provided a display element based on polymers and/or low molecular-weight organic materials by a fluorescent quenching effect due to an electric field. The display element is adapted to operate in an organic light-emitting diode display (OLED) mode under dark ambient light and in a field quenching photoluminescence emission device (FQPED) mode under bright ambient light, the latter working based on the fluorescent quenching effect due to an electric field.
According to the display element addressing method and the display element of the present invention, the OLED mode is selected under dark ambient light and the FQPED mode is selected under bright ambient light. Accordingly, the light emitted from the OLED display can be prevented from being weakened due to the light from an external light source. For example, even under intense sunlight, the contrast of the OLED display increases. Therefore, in disregard of a change in the intensity of ambient light, the contrast can be maintained at a constant level. Also, power consumption can be reduced by using the FQPED mode.